(SQL Server) Dropbox Content Hash

Demonstrates how to compute the Dropbox content_hash of a file. (This is the "content_hash" found in the Dropbox FileMetadata object.

Note: This example requires Chilkat v9.5.0.79 or greater because it uses the fac.ReadBlockBd method.

For more information, see https://www.dropbox.com/developers/reference/content-hash

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

// Important: See this note about string length limitations for strings returned by sp_OAMethod calls.
//
CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr int
    DECLARE @sTmp0 nvarchar(4000)
    -- This example requires the Chilkat API to have been previously unlocked.
    -- See Global Unlock Sample for sample code.

    DECLARE @crypt int
    EXEC @hr = sp_OACreate 'Chilkat_9_5_0.Crypt2', @crypt OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    -- To calculate the content_hash of a file:
    -- Split the file into blocks of 4 MB (4,194,304 or 4 * 1024 * 1024 bytes). The last block (if any) may be smaller than 4 MB.
    -- Compute the hash of each block using SHA-256.
    -- Concatenate the hash of all blocks in the binary format to form a single binary string.
    -- Compute the hash of the concatenated string using SHA-256. Output the resulting hash in hexadecimal format.

    EXEC sp_OASetProperty @crypt, 'HashAlgorithm', 'sha256'
    EXEC sp_OASetProperty @crypt, 'EncodingMode', 'hex_lower'

    -- We're going to calculate the content_hash for the Milky Way JPG image linked here:  https://www.dropbox.com/developers/reference/content-hash

    DECLARE @fac int
    EXEC @hr = sp_OACreate 'Chilkat_9_5_0.FileAccess', @fac OUT

    DECLARE @bd int
    EXEC @hr = sp_OACreate 'Chilkat_9_5_0.BinData', @bd OUT

    DECLARE @bdHashes int
    EXEC @hr = sp_OACreate 'Chilkat_9_5_0.BinData', @bdHashes OUT

    DECLARE @success int
    EXEC sp_OAMethod @fac, 'OpenForRead', @success OUT, 'qa_data/jpg/milky-way-nasa.jpg'
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @fac, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @crypt
        EXEC @hr = sp_OADestroy @fac
        EXEC @hr = sp_OADestroy @bd
        EXEC @hr = sp_OADestroy @bdHashes
        RETURN
      END

    DECLARE @blockSize int
    SELECT @blockSize = 4194304
    DECLARE @numBlocks int
    EXEC sp_OAMethod @fac, 'GetNumBlocks', @numBlocks OUT, @blockSize

    DECLARE @i int
    SELECT @i = 0
    WHILE (@i < @numBlocks)
      BEGIN
        -- Read the next 4MB block into bd.
        EXEC sp_OAMethod @bd, 'Clear', @success OUT
        EXEC sp_OAMethod @fac, 'ReadBlockBd', @success OUT, @i, @blockSize, @bd

        DECLARE @hashHex nvarchar(4000)
        EXEC sp_OAMethod @crypt, 'HashBdENC', @hashHex OUT, @bd


        PRINT @i + ': ' + @hashHex
        EXEC sp_OAMethod @bdHashes, 'AppendEncoded', @success OUT, @hashHex, 'hex_lower'

        SELECT @i = @i + 1
      END

    EXEC sp_OAMethod @fac, 'FileClose', NULL

    -- Hash the concatenated SHA-256 hashes.
    DECLARE @content_hash nvarchar(4000)
    EXEC sp_OAMethod @crypt, 'HashBdENC', @content_hash OUT, @bdHashes

    PRINT 'content_hash = ' + @content_hash

    EXEC @hr = sp_OADestroy @crypt
    EXEC @hr = sp_OADestroy @fac
    EXEC @hr = sp_OADestroy @bd
    EXEC @hr = sp_OADestroy @bdHashes


END
GO